Catalytic cracking catalysts and catalytic cracking processes are well known in the patent and scientific literature. Such literature has largely dealt with the preparation of modified zeolites for use as cracking catalysts. The following patents are representative of the prior art.
The use of conversion catalysts formed from a zeolite dispersed in a siliceous matrix has been disclosed in U.S. Pat. No. 3,140,249 and U.S. Pat. No. 3,352,796.
The use of blended matrix components, e.g., a catalyst comprising a zeolite, an inorganic oxide matrix and inert fines, which may be alpha alumina, is disclosed in U.S. Pat. No. 3,312,615. Catalysts comprising an amorphous silica-alumina, separately added alumina and a zeolite are disclosed in U.S. Pat. No. 3,542,670 and catalyst comprising a zeolite, an amorphous hydrous alumina and alumina monohydrate are disclosed in U.S. Pat. No. 3,428,550.
It has been disclosed that the steam and thermal stability of zeolites can be improved by the use of zeolites having a low level of alkali metal content and a unit cell size less than about 24.45 Angstroms (See: U.S. Pat. Nos. 3,293,192 and Re. 28,629 (Reissue of U.S. Pat. No. 3,402,996)).
Further, it has been disclosed (U.S. Pat. No. 3,591,488) that the hydrogen or ammonium form of a zeolite may be treated with H.sub.2 O at a temperature ranging from about 800.degree. to about 1500.degree. F., and then subsequently cation exchanging the steam and water treated zeolite with cations which may be rare earth metal cations. The method increases the silica to alumina mole ratio of the zeolite crystal framework lattice and also crystal structure imperfections. U.S. Pat. No. 3,676,368 discloses a rare earth exchanged-hydrogen faujasite containing from 6 to 14 percent rare earth oxides. U.S. Pat. No. 3,957,623 discloses a rare earth exchanged zeolite having a total of 1 to 10 weight percent rare earth metal oxide. U.S. Pat. No. 3,607,043 discloses a process for preparing a zeolite having a rare earth content of 0.3 to 10 weight percent.
U.S. Pat. No. 4,036,739 discloses hydrothermally stable and ammonia stable Y zeolite in which a sodium Y zeolite is ion exchanged to partially exchange sodium ions for ammonium ions, followed by steam calcination and a further ion exchange with ammonium to reduce the final sodium oxide content to below 1 weight percent, followed by calcination of the reexchanged product, or according to U.S. Pat. No. 3,781,199, the second calcination may be conducted after the zeolite is admixed with a refractory oxide.
The recent interest in high octane gasoline has resulted in the development of catalyst systems directed to improvement in the octane number of the products of catalytic cracking processes. For example, U.S. Pat. Nos. 3,758,403, 3,894,931, 3,984,933, 3,894,934 and 4,309,280 relate to cracking catalysts containing ZSM-5 type zeolites as catalyst components.
In addition to the above, a new approach to the improvement of cracking catalysts has been the development of new zeolitic aluminosilicates capable of providing unique properties when employed in cracking catalysts. One such family of new zeolitic aluminosilicates is disclosed in E.P.C. Application Publication No. 82,111 published June 28, 1983 and in U.S. Pat. No. 4,503,023. The use of rare earth exchanged forms of such zeolitic aluminosilicates is disclosed in copending U.S. Ser. No. 490,965, filed May 2, 1983 now U.S. Pat. No. 4,687,754. Although such copending application generally discloses rare earth exchanged zeolites, such does not disclose catalysts having critical amounts of rare earth cation and Na.sub.2 O, as claimed by the instant invention, whereby gasoline products having improved octane number are obtained.
The instant invention relates to an improved process for upgrading the octane number of the gasoline products from catalytic cracking processes.